1. Field of the Invention
The present invention relates generally to apparatus for and a method of driving an ultrasonic horn, and particularly to a scheme in which the resonant frequency of the horn in an operating environment is determined periodically, and the frequency of a horn drive signal is adjusted to correspond to the determined resonant frequency of the horn.
2. Description of the Known Art
Ultrasonic horns are employed in clinical analyzers of the kind in which a series cuvettes pass on belt means through a temperature controlled liquid bath, so as to bring liquid solutions contained in the cuvettes up to the bath temperature. The horn serves to dissolve solid reagent tablets in the liquid solutions in the cuvettes while the belt means conveys the cuvettes within the operating region of the horn. Further details of an ultrasonic horn suitable for use in a clinical analyzer liquid bath can be found in U.S. patent application Ser. No. 697,277, filed Feb. 1, 1985, and assigned to the assignee of the present invention.
In the known systems, the horn is driven by a signal of fixed frequency corresponding to an assumed resonant frequency for the horn. It will be appreciated that maximum efficiency is obtained, i.e., ultrasonic waves produced by the horn are of greatest amplitude for a certain fixed amplitude of the drive signal, when the drive signal frequency is matched to the resonant frequency of the horn in an actual operating environment. It will also be understood that if a resonant frequency for the horn is determined at the time of manufacture, and drive circuitry for the horn is adjusted to match the determined resonant frequency, the operating environment in which the horn is placed, i.e., air or liquid, varying temperatures, and different densities of liquid solutions in cuvettes moving in the operating region of the horn, all will act to change the initially assumed resonant frequency.
As far as is known, there has not been proposed any process or system for operating an ultrasonic horn in a changing environment while actively tracking the resonant frequency of the horn and effecting a corresponding adjustment in the frequency of the drive signal for the horn.